The present invention relates generally to gas turbine engines, and, more specifically, to fan blades therein.
A turbofan gas turbine engine configured for powering an aircraft in flight includes a row of large fan blades extending radially outwardly from a supporting rotor disk. The fan is surrounded by an annular casing supported in a corresponding nacelle. The casing defines an outer flowpath boundary for channeling air through the fan blades, and inner platforms are disposed at the root of the blades for defining the radially inner flowpath boundary.
Fan blades typically include a substantial amount of angular twist between the tip and root of the airfoil over which the air is channeled during operation. The airfoil tip thusly extends both axially and circumferentially due to the substantial twist, and correspondingly has a generally convex outer profile for maintaining a substantially uniform and small radial gap between the tip and the casing along the entire axial or chordal extent of the tip between its leading and trailing edges.
In one type of fan blade, a plurality of anchor tangs extend radially inwardly from the root end of the airfoil, below an integral platform thereat, and are interdigitated with a plurality of corresponding annular rims formed in the supporting disk. The tangs and rims have coaxially aligned apertures through which a corresponding retention pin is disposed for pivotally mounting each blade to the disk. This pin joint anchoring configuration is aligned with the stacking axis of the airfoil for carrying centrifugal loads generated during operation through the pin and into the supporting disk.
Conventional anchor tangs have generally semicircular inboard profiles at their radial lower ends to eliminate extraneous material and corresponding weight which does not contribute to the strength of the tangs for accommodating the substantial centrifugal loads generated during operation. Accordingly, the individual blades are thus free to pivot around the pins during assembly until the full complement row of fan blades is installed, with the adjacent fan blades then restraining pivotal movement of its neighbors.
Since fan blades have relatively thin tips and leading and trailing edges, the corresponding airfoil corners at the opposite ends of the tip are relatively thin and sharp. Excessive pivoting of the fan blade during assembly can cause either tip corner to impact the inner surface of the surrounding fan casing. This impact can cause damage either to the blade tip itself or to the inner surface of the fan casing, and is therefore undesirable.
In order to limit or restrain pivoting of the individual blades during assembly, a pivot limiting feature is typically incorporated in the blades. In one configuration, tip pivoting is prevented by providing extra material between a pair of the anchor tangs directly above the outer surface of the corresponding disk rim. This extra material defines a small gap with the rim perimeter and abuts the disk perimeter when the blade begins to tilt or pivot around its retention pin. In this way, the opposite ends of the blade tip are prevented from contacting the fan casing during assembly.
However, the extra material required between the two anchor tangs adds to the weight of the blade at the underside of the platform. That extra weight introduces a corresponding increase in centrifugal force during operation which correspondingly requires a suitably strong platform and anchor tangs for withstanding the loads. The centrifugal loads generate corresponding stresses in the tangs, pins, and disk during operation which affect the useful life of the fan.
Accordingly, it is desired to provide an improved fan having reduced blade weight and associated centrifugal forces during operation, with an improved anti-pivoting feature for assembly.
A fan blade includes perforated anchor tangs, one with inboard corners and the remainder without. The corners are disposed in a complementary seat in a rotor disk for limiting blade pivoting during assembly.